The thermite reaction has been utilized for a long period of time in order to provide weldments normally associated with the railroad industry and in electric power transmission. The thermite reaction is comprised of a reaction between aluminum (A1) and a metal oxide wherein the metal oxide is reduced providing a filler metal, i.e., the source of the filler metal is the oxide on reduction. The "Goldschmidt" reaction is the basis of the application of the process described in U.S. Pat. No. 2,229,045 to Charles A. Cadwell. This reaction is as follows: ##STR1##
The "Goldschmidt" reaction has been successfully utilized over the years to weld or join metals such as iron (Fe) and copper (Cu). However, the process is not particularly well adapted for use in joining metals such as aluminum (A1) wherein the use of a copper (Cu) or iron (Fe) filler metal is generally unacceptable.
U.S. Pat. No. 3,020,610 to Rejdak discloses a method of welding aluminum (A1) and other metals, and provides a listing of various reactions which can be utilized to produce reaction products which may be utilized to provide a weldment. Unfortunately, in the method disclosed by Rejdak the weld which is formed is not suitable for some applications. More particularly, the weld metal formed by the Rejdak method is not chemically pure enough for some applications. For example, a weldment produced by the Rejdak method in some environments may be susceptible to a high level of corrosion due to the presence of impurities or unwanted elements in the resultant weldment.
U.S. Pat. No. 2,569,956 to Schiltknecht discloses a process wherein a thermite reaction is utilized to join together a pair of non-ferrous metal pieces by melting a sleeve about the metal pieces. This process is usually referred to as the "Alusuisse Process" referring to a welding system produced by Swiss Aluminum Ltd. of Zurich. Unfortunately, the "Alusuisse Process" is an indirect welding process (i.e., the heat generated by the thermite reaction does not produce a weld filler metal by chemical reaction) and it is not suitable for use in some joining applications.